Sometimes it is too hard to say what needs to be said.
For example, it is not always possible to have important conversations while someone is still alive. Perhaps it is too difficult to share the memory, praise, or apology that is needed. Or the opportunity never arises, or death comes unexpectedly.
Alternatively, the other person may be alive, and there is an apology or praise that we have an opportunity to share, but doing so in a conversation is too stressful. For example, apologizing after an argument, or sharing praise.
When we are prevented from saying what we want or need to say, the unsaid things build up. The result is anxiety, regret, and a feeling of failure.
What is needed is a way of letting go of a memory, apologizing after an argument, or giving feedback to someone, it is impossible or difficult for us to do.